1. Field of the Invention
The present invention relates to telecommunications networks, and more particularly, to a routing of a call through a telecommunications network based on a probability distribution. The present invention is especially suited for use with enhanced 911 (E911) emergency telephone service.
2. Description of the Prior Art
A conventional public telephone network for a particular geographic service area includes an end office and a plurality of switches known as tandems. The end offices are coupled to each of the tandems via a trunk. When a call originates from a telephone coupled to one of the end offices, the call is routed to one of the tandems, referred to as the primary tandem, and thereafter directed to a destination office. Depending on the nature of the call, the destination office may be in the same geographic service area, or in a different geographic service area.
If all of the trunks from an end office to the primary tandem are in use or maintenance busy, this condition will be recognized by the end office. If an additional call occurs that would ordinarily be routed to the primary tandem, the call will be re-routed to a secondary tandem, and thereafter directed to the destination office. The re-routing is thus triggered by a non-availability of the trunk from the end office to the primary tandem. However, if the trunk from the end office to the primary tandem is available, but the primary tandem experiences a malfunction that prevents a completion of the call, then the re-routing of the call to the secondary tandem will not be triggered. Consequently, a caller could repeatedly attempt to place a call, but the call would be blocked at the malfunctioning primary tandem.
After service personnel recognize a malfunction of the primary tandem, they can alter the operation of the end office so that no calls are routed from the end office to the faulty primary tandem. Instead the calls will be routed to the secondary tandem.
In practice, most public telephone networks include a plurality of end offices, each of which is coupled to a plurality of tandems. Consequently, when a malfunction of a tandem requires a change at an end office, the change must be made at each of the end offices that are coupled to the tandem.
An incompletion of a call is always objectionable. However, it is particularly serious in a case where the call is for an emergency service, such as in the case of an enhanced 911 (E911) call. E911 telephone service allows a person to call for emergency assistance by dialing 911 from a telephone. The E911 call is routed to an E911 Public Safety Answering Point (PSAP) typically located in a firehouse, police department or other designated location that services the area from which the call originated. The incompletion of an E911 call can delay the response to the emergency. The consequence of such a delay could be very serious or grave.
It is an object of the present invention to provide an improved method for routing a call through a telecommunications network.
It is another object of the present invention to provide such a method in which a call from a particular geographic service region is randomly routed to one of a plurality of tandem switches.
It is another object of the present invention to provide such a method that conveniently prohibits a routing of calls to a malfunctioning tandem switch.
It is a further object of the present invention to provide such a method in which a distribution of calls routed through a plurality of end offices to a plurality of tandem switches can be redefined at a central location rather than at each end office.
These and other objects of the present invention are achieved by a method for routing a call through a telecommunications network, comprising the steps of (a) receiving a prompt, from one of a plurality of service switching points in a predetermined geographic service area, for a service associated with the call, and (b) determining one of a plurality of tandem switches to which the call will be directed based on a probability distribution.